Elastomeric segment polymers are understood to be polymers which are composed of units constituted by "soft segments" and "hard segments" or "rigid segments". Polymers of this kind possess very interesting properties one of the most important of which is a high extensibility and reversibility after dilation. As an example of this type of segmented polymer there may be mentioned the so-called Spandex fibers in which "hard" segments consisting of urethane or urethane-urea are joined to "soft" polyester or polyether segments.
Various methods are known for making elastomeric polymers of the above type. Diisocyantes are generally used as coupling agents for diols and other difunctional polymers. Thus, for example, in U.S. Pat. No. 3,386,932 a low molecular weight polyester or polyether is joined by means of a diisocyanate to a segment obtained by depolymerizing cellulose triacetate, the segment having hydroxyl end groups and a molecular weight on the order of 3000 to 4000. This method results in the production of a segment polymer which is suitable for casting into clear, elastic and rigid films as provided for in U.S. Pat. No. 3,386,930.
The segmented polymer produced according to U.S. Pat. No. 3,386,932 starting with cellulose triacetate segments which are subsequently deacetylated whereby a product containing free hydroxyl groups is obtained has been considered to be suitable for use as a biodegradable polymer (Journal of Polymer Sciences, Polymer Letters Edition, vol. 11 (1973), pages 731-735). The method provides for the use of segments obtained by depolymerizing cellulose triacetate and which have a molecular weight between 1000 and 5000 and in which the free hydroxyl groups are acetylated. The end product is then deacetylated to thereby regain free hydroxyl groups. The procedure is complicated and the uses to which the product can be put are limited.